Oilfield operations can require a great quantity of information relating to the parameters and conditions encountered downhole. Downhole logging tools can collect or log such information by performing ‘logging while drilling’ (LWD) or wireline logging. With wireline logging, a probe or ‘sonde’ is lowered into the borehole after some or the entire well has been drilled. The sonde can hang at the end of a long cable or ‘wireline’ that provides mechanical support to the sonde as well as providing an electrical connection between the sonde and electrical equipment located at the surface of the well. With LWD, the drilling assembly includes sensing instruments that measure various parameters as an earth formation is being penetrated. While LWD allows more contemporaneous formation measurements, drilling operations result in environments where large or resource intensive electronic instrumentation and sensors are typically not desirable.
A numerically controlled oscillator (NCO) is a digital signal generator that creates a synchronous (e.g., clocked), discrete-time, discrete-valued representation of a waveform, where the waveform is typically sinusoidal. An NCO can be used in conjunction with a digital-to-analog converter (DAC) to create an analog output signal. An NCO can be used in communications and signal processing instruments. An NCO offers high output bandwidth, fine frequency resolution, and fast tuning speed. For many use cases and applications, such as oilfield operations, the phase drift and jitter of an NCO is desired to be extremely small, such that NCO designs are very complex.
An NCO can generate a frequency and phase tunable output signal with a precision fixed-frequency clock. In time domain, the output frequency of an NCO is a function of the system clock. In the realization of an NCO, there are two conflicting aspects to that need to be addressed, namely phase accuracy and resource consumption. In order to maintain acceptable levels of phase accuracy at high frequencies, resource and power consumption usually needs to be very high. Conversely, in order to reduce or minimize resource and power consumption, usually NCOs sacrifice phase accuracy.